Directed synthesis of a hybrid improper magnetoelectric multiferroic material

Preparing materials which simultaneously exhibit spontaneous magnetic and electrical polarisations is challenging as the electronic features which are typically used to stabilise each of these two polarisations in materials are contradictory. Here we show that by performing low-temperature cation-exchange reactions on a hybrid improper ferroelectric material, Li₂SrTa₂O₇, which adopts a polar structure due to a cooperative tilting of its constituent TaO₆ octahedra rather than an electronically driven atom displacement, a paramagnetic polar phase, MnSrTa₂O₇, can be prepared. On cooling below 43 K the Mn²⁺ centres in MnSrTa₂O₇ adopt a canted antiferromagnetic state, with a small spontaneous magnetic moment. On further cooling to 38 K there is a further transition in which the size of the ferromagnetic moment increases coincident with a decrease in magnitude of the polar distortion, consistent with a coupling between the two polarisations.